Protective control device for differential gear device

Abstract

To provide a protection control device of a differential gear device capable of adopting inexpensive surface treatment for a sliding part while suppressing seizure.SOLUTION: The electronic control device 70 includes a stuck state determining portion 74 configured to determine whether the hybrid vehicle 10 is in the stuck state, and a continuously-differential determining portion 76 configured, when the stuck state determining portion 74 determines that the hybrid vehicle 10 is in the stuck state, to determine whether the hybrid vehicle 10 is in a continuously-differential state in which the oil temperature Toil is equal to or lower than the predetermined temperature TA, the accumulated heat generation amount Q in the first predetermined time period T1 is equal to or larger than the predetermined heat generation amount QA, and the front-wheel rotation speed difference Δ Nwf is equal to or larger than the predetermined value N1 for a second predetermined time period T2 or longer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a protection and control device for a differential gear device of a vehicle. [Background technology]

[0002] Patent Document 1, for example, discloses a control device for a vehicle equipped with a differential gear unit that, when it detects a stuck state in which driving force is lost, strengthens the differential limit of the differential gear unit to escape the stuck state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-196929 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the differential gear device continues to rotate differentially when escaping from a stuck state, the sliding parts of the differential gear device may become hot and seize, which may lead to seizure. To prevent seizure in the differential gear device, a control (hereinafter referred to as protective control) is implemented by monitoring the rotational speed difference absorbed by the differential gear device and suppressing the vehicle's drive output to prevent seizure of the sliding parts when the rotational speed difference exceeds a threshold and continues for a threshold period, i.e., when the differential gear device is under high load. However, this method does not implement protective control for the temperature rise that occurs when differential rotation continues for a long period of time with a low rotational speed difference when escaping from a stuck state, making it an insufficient measure to prevent seizure. Furthermore, when the oil temperature in the differential gear device is low, the viscosity of the lubricating oil decreases, causing oil shortage and seizure. To address this issue, a surface treatment is applied to the sliding parts to prevent seizure even under nearly unlubricated conditions, which increases the cost of the differential gear device.

[0005] The present invention has been made in light of the above circumstances, and its object is to provide a protection and control device for a differential gear unit that can employ inexpensive surface treatment for the sliding parts while suppressing seizure. [Means for solving the problem]

[0006] The gist of the present invention is a protection and control device for a differential gear device that absorbs the difference in rotational speed between the left and right drive wheels of a vehicle, comprising: (a) a stuck determination unit that determines whether the vehicle is in a stuck state in which it has lost its driving force; (b) a differential continuation determination unit that, when the stuck determination unit determines that the vehicle is in a stuck state, determines whether the vehicle is in a differential continuation state in which the oil temperature in the differential gear device is below a predetermined temperature, the cumulative heat generation amount of the differential gear device over a first predetermined period is equal to or greater than a predetermined heat generation amount, and the rotational speed difference between the left and right drive wheels is equal to or greater than a predetermined threshold and has continued for equal to or greater than a second predetermined period; and (c) an output suppression control unit that suppresses the drive output of the vehicle when the differential continuation determination unit determines that the vehicle is in a differential continuation state. [Effects of the Invention]

[0007] The differential gear protection and control device of the present invention includes a stuck determination unit that determines whether the vehicle is in a stuck state in which driving force is lost; a differential continuation determination unit that, if the stuck determination unit determines that the vehicle is in a stuck state, determines whether the vehicle is in a differential continuation state in which the oil temperature in the differential gear is below a predetermined temperature, the cumulative heat generation amount of the differential gear over a first predetermined period is equal to or greater than a predetermined heat generation amount, and the rotational speed difference between the left and right drive wheels is equal to or greater than a predetermined threshold and has continued for at least a second predetermined period; and an output suppression control unit that suppresses the drive output of the vehicle if the differential continuation determination unit determines that the vehicle is in a differential continuation state. Thus, even if, upon escaping from the stuck state determined by the stuck determination unit, differential rotation continues for a long period with a low rotational speed difference and the oil temperature in the differential gear is low, the differential continuation determination unit determines that the vehicle is in a differential continuation state, so that the output suppression control unit suppresses the drive output of the vehicle and prevents seizure of the sliding parts. Therefore, it is possible to provide a differential gear protection and control device that enables the use of inexpensive surface treatments for the sliding parts while preventing seizure. Furthermore, suppression of drive output is limited to special conditions, such as when the vehicle is stuck, differential rotation continues for a long period of time with a low rotational speed difference, and the oil temperature in the differential gear device is low, so suppression of drive output can minimize the frequency at which the driver is reminded of engine malfunction. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a vehicle according to an embodiment of the present invention, and is also a functional block diagram showing the main control functions of an electronic control device that performs protection control of a differential gear device. [Figure 2] 10 is an example of a flowchart illustrating a control operation of a conventional electronic control device. [Figure 3] 3 is an example of a flowchart illustrating a control operation of an electronic control device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. [Example]

[0010] FIG. 1 is a schematic diagram of a vehicle 10 according to an embodiment of the present invention, and is also a functional block diagram showing the main control functions of an electronic control device 70 that performs protection control of a differential gear unit.

[0011] The vehicle 10 includes an engine 12, front wheels 14 (14L, 14R), rear wheels 16 (16L, 16R), a first power transmission path between the engine 12 and the front wheels 14, and a second power transmission path between the engine 12 and the rear wheels 16. The vehicle 10 is a 4WD vehicle based on a front-mounted engine, front-wheel drive (FF) system.

[0012] The engine 12 is a power source for driving the vehicle and is a well-known internal combustion engine. The engine torque Te, which is the output torque of the engine 12, is controlled by an electronic control device 70. The front wheels 14 are main drive wheels and serve as drive wheels in both two-wheel drive (=2WD) and four-wheel drive (=4WD) driving modes. The rear wheels 16 are auxiliary drive wheels and serve as driven wheels in 2WD driving modes and as drive wheels in 4WD driving modes. The first power transmission path is provided, in order from the engine 12 side, with an automatic transmission 18, a front wheel differential gear device 20, a pair of front wheel axles 22, and the like, which are well-known components. The second power transmission path includes an automatic transmission 18, a transfer case 24 which is a front / rear wheel power distribution device that distributes a portion of the power of the engine 12 transmitted to the front wheels 14 to the rear wheels 16, a propeller shaft 28 which transmits the power from the engine 12 distributed by the transfer case 24 to the rear wheels 16 during 4WD driving, a rear wheel differential gear device 32, a pair of couplings 36, and a pair of rear wheel axles 34, all of which are well known components. The front wheels 14 and the front wheel differential gear device 20 correspond to the "left and right drive wheels" and the "differential gear device" of the present invention, respectively.

[0013] 1 shows the transfer case 24 in a state during 4WD driving. The power of the engine 12 distributed by the transfer case 24 is transmitted to the rear wheels 16 via the propeller shaft 28, the rear differential gear device 32, a pair of couplings 36, and a pair of rear axles 34. The pair of couplings 36 are well-known electronically controlled couplings. The pair of couplings 36 each have a controlled transmission torque capacity.

[0014] In the vehicle 10, for example, when the transfer 24 is in a state in which it can distribute a portion of the power of the engine 12 to the rear wheels 16 and the transmission torque capacities of the pair of couplings 36 are controlled to a value greater than zero, driving force is also transmitted to the rear wheels 16 in accordance with the transmission torque capacities of the pair of couplings 36. This achieves 4WD driving. In 4WD driving, the torque distribution between the front wheels 14 and the rear wheels 16 is adjusted by controlling the transmission torque capacities of the pair of couplings 36.

[0015] The vehicle 10 is equipped with an electronic control device 70 as a control device that controls each part of the vehicle 10. The electronic control device 70 is configured to include a so-called microcomputer. The electronic control device 70 corresponds to the "protection control device" of the present invention.

[0016] The electronic control device 70 receives various signals (e.g., engine speed Ne of the engine 12, front wheel speed Nwf (wheel speeds Nwfl, Nwfr of the front wheels 14L, 14R), rear wheel speed Nwr (wheel speeds Nwrl, Nwrr of the rear wheels 16L, 16R), accelerator opening θacc, steering angle θsw, oil temperature Toil in the front wheel differential gear device 20, and a driver-initiated 4WD driving selection signal 4WDon) based on detected values ​​from various sensors provided on the vehicle 10 (e.g., vehicle condition sensor 80, wheel speed sensors 82, accelerator opening sensor 84, steering sensor 86, differential temperature sensor 88, 4WD selection switch 90, etc.). The front wheel speed Nwf is, for example, an average value of the wheel speeds Nwfl, Nwfr. The rear wheel speed Nwr is, for example, an average value of the wheel speeds Nwrl, Nwrr. The front wheel differential rotation speed ΔNwf (ΔNwf = |Nwfl - Nwfr|), which is the difference between the wheel speeds Nwfl and Nwfr, is absorbed by the front wheel differential gear device 20. Also, the rear wheel differential rotation speed ΔNwr (ΔNwr = |Nwrl - Nwrr|), which is the difference between the wheel speeds Nwrl and Nwrr, is absorbed by the rear wheel differential gear device 32. The front wheel differential rotation speed ΔNwf corresponds to the "difference in rotation speed between the left and right drive wheels" of the present invention.

[0017] The electronic control device 70 outputs various command signals (e.g., an engine control signal Se for controlling the engine 12, a shift control signal Sat for controlling the shifting of the automatic transmission 18, a transfer control signal Str for alternatively selecting between 2WD driving and 4WD driving, torque control signals Sc1 and Sc2 for controlling the transmission torque capacity of the pair of couplings 36, etc.) to each device provided in the vehicle 10 (e.g., the engine 12, the automatic transmission 18, the transfer 24, the pair of couplings 36, etc.).

[0018] The electronic control device 70 also functionally includes a high load determination unit 72, a stuck determination unit 74, a differential continuation determination unit 76, and an output suppression control unit 78 for carrying out protective control of the front wheel differential gear device 20.

[0019] FIG. 2 is an example of a flowchart illustrating a conventional example of control operation of the protection control performed by the electronic control unit 70, which is executed repeatedly while the vehicle 10 is traveling, for example.

[0020] First, in step S1 (hereinafter, "step" will be omitted) corresponding to the function of the high load determination unit 72, it is determined whether the front wheel differential rotation speed ΔNwf of the front wheels 14 (14L, 14R), which are the left and right drive wheels of the vehicle 10, is equal to or greater than the high load threshold Nh and has continued for equal to or greater than the high load determination period Th. The high load threshold Nh and the high load determination period Th are set in advance by design or experimentation as appropriate values ​​for preventing seizure of the sliding parts due to a temperature rise when the front wheel differential gear device 20 is under a high load. If the determination in S1 is negative, the routine is terminated. If the determination in S1 is positive, the engine rotation speed Ne, which is the drive output of the vehicle 10, is reduced in S2, which corresponds to the function of the output reduction control unit 78, and the routine is terminated. By reducing the engine rotation speed Ne, the front wheel differential rotation speed ΔNwf, i.e., the differential rotation of the front wheel differential gear device 20, is also reduced, and seizure of the sliding parts is reduced.

[0021] However, in the conventional protective control, when escaping from a stuck state in which the vehicle 10 has lost its driving force, protective control is not executed against the temperature rise that occurs when differential rotation continues for a long period of time at a low rotational speed difference (low front wheel differential rotation speed ΔNwf), and this is an insufficient measure to prevent seizure. Also, under conditions where the oil temperature Toil in the front wheel differential gear device 20 is low, the viscosity of the lubricating oil decreases, causing oil shortage and making seizure more likely. As a countermeasure to this, a surface treatment is employed on the sliding parts that prevents seizure even under conditions close to no lubrication, which also poses the problem of increasing the cost of the front wheel differential gear device 20.

[0022] FIG. 3 is an example of a flowchart illustrating the control operation of the protection control performed by the electronic control unit 70 according to the embodiment of the present invention, which is executed repeatedly while the vehicle 10 is traveling, for example.

[0023] First, in S10, which corresponds to the function of the high load determination unit 72, it is determined whether the front wheel differential rotation speed ΔNwf is equal to or greater than the high load threshold value Nh and has continued for equal to or greater than the high load determination period Th. This is the same control operation as S1 in Fig. 2. If the determination in S10 is positive, the engine rotation speed Ne, which is the drive output of the vehicle 10, is reduced in S40, which corresponds to the function of the output reduction control unit 78, and this routine is terminated. That is, the same control operation as in Fig. 2 (conventional example) is executed.

[0024] If the determination in S10 is negative, in S20, which corresponds to the function of the stuck determination unit 74, it is determined whether or not the vehicle 10 is stuck and has lost its driving force. This determination is made, for example, as shown in a balloon in S20 in FIG. 3 , by determining whether or not one of the following conditions is met: when the vehicle 10 is running in 2WD, the front wheel differential rotation speed ΔNwf is equal to or greater than a predetermined threshold value N1 and the rear wheel speed Nwr is less than 2 km / h; or when the vehicle 10 is running in 4WD, the front wheel differential rotation speed ΔNwf is equal to or greater than a predetermined threshold value N1 and the rear wheel differential rotation speed ΔNwr is equal to or greater than a rear wheel differential threshold value N2. The predetermined threshold value N1 and the rear wheel differential threshold value N2 are each set in advance by design or experimentation to appropriate values ​​that allow a determination to be made that the front wheel differential gear device 20 is stuck even when it is in a low load state, i.e., a state with a low differential rotation speed. For example, the predetermined threshold value N1 is set to a value equal to or less than the high load threshold value Nh. Also, for example, the rear wheel differential threshold N2 corresponding to the auxiliary drive wheels during 4WD driving is set to a value equal to or less than the predetermined threshold N1. If the determination in S20 is negative, this routine is ended.

[0025] If the determination in S20 is positive, in S30, which corresponds to the function of the differential continuation determination unit 76, it is determined whether the oil temperature Toil in the front wheel differential gear device 20 is equal to or lower than a predetermined temperature TA and / or the cumulative heat generation amount Q of the front wheel differential gear device 20 in a first predetermined period T1 is equal to or higher than a predetermined heat generation amount QA, and the front wheel differential rotation speed ΔNwf is equal to or higher than a predetermined threshold value N1 and has continued for at least a second predetermined period T2. The cumulative heat generation amount Q can be found, for example, by sequentially calculating the value of the following equation (1) in the first predetermined period T1. ∫α×ΔNwfdt (1) Here, α is a coefficient for calculating the amount of heat generated. The predetermined temperature TA is set in advance by design or experimentation as an appropriate value for preventing seizure in an oil-out state caused by a decrease in lubricating oil viscosity when the oil temperature Toil is low. The predetermined heat generation amount QA, the first predetermined period T1, and the second predetermined period T2 are set in advance by design or experimentation as appropriate values ​​for preventing seizure in the sliding parts due to a temperature rise caused by long-term operation of the front wheel differential gear device 20 at a low load, i.e., when differential rotation continues for a long period at a low differential rotation speed. If the determination in S30 is negative, the routine is terminated.

[0026] If the determination in S30 is positive, the engine rotation speed Ne, which is the driving output of the vehicle 10, is reduced in S40, which corresponds to the function of the output reduction control unit 78, and this routine is then terminated.

[0027] The electronic control device 70 of this embodiment includes a stuck determination unit 74 that determines whether the vehicle 10 is in a stuck state in which it has lost its driving force, a differential continuation determination unit 76 that, when the stuck determination unit 74 determines that the vehicle 10 is in a stuck state, determines whether the vehicle is in a differential continuation state in which the oil temperature Toil in the front wheel differential gear device 20 is below a predetermined temperature TA and / or the cumulative heat generation amount Q of the front wheel differential gear device 20 over a first predetermined period T1 is above a predetermined heat generation amount QA, and the front wheel differential rotation speed ΔNwf is above a predetermined threshold N1 and has continued for at least a second predetermined period T2, and an output suppression control unit 78 that suppresses the drive output of the vehicle 10 when the differential continuation determination unit 76 determines that the vehicle is in a differential continuation state. As a result, when escaping from a stuck state determined by the stuck determination unit 74, even if both or at least one of the following conditions are met: differential rotation continues for a long period of time at a low rotational speed difference; and the oil temperature Toil in the front wheel differential gear unit 20 is low, the differential continuation determination unit 76 determines that the differential state is continuing, and the output suppression control unit 78 suppresses the engine rotation speed Ne, which is the drive output of the vehicle 10, and seizure of the sliding parts is suppressed. Therefore, a differential gear unit protection and control device is provided that can employ inexpensive surface treatment for the sliding parts while suppressing seizure. Furthermore, because the suppression of the drive output is limited to the case where the vehicle 10 is stuck and differential rotation continues for a long period of time at a low rotational speed difference; and the oil temperature Toil in the front wheel differential gear unit 20 is low; the suppression of the engine rotation speed Ne minimizes the frequency at which the driver is reminded of engine malfunction.

[0028] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention can also be applied to other embodiments.

[0029] For example, in the above-described embodiment, the vehicle 10 is a 4WD vehicle in which the front wheels 14 are the main drive wheels and the rear wheels 16 are the auxiliary drive wheels or driven wheels, but the present invention can also be applied to a 4WD vehicle in which the rear wheels are the main drive wheels and the front wheels are the auxiliary drive wheels or driven wheels.Furthermore, by applying the 2WD running case of the above-described embodiment, the present invention can also be applied to a 2WD vehicle in which only the front wheels or the rear wheels are driven wheels.

[0030] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art. [Explanation of symbols]

[0031] 10: vehicle, 14: front wheels (left and right drive wheels), 20: front wheel differential gear device (differential gear device), 70: electronic control device (protection control device), 74: stuck determination unit, 76: differential continuation determination unit, 78: output suppression control unit, N1: predetermined threshold, Ne: engine rotation speed (drive output), Q: cumulative heat generation amount, QA: predetermined heat generation amount, T1: first predetermined period, T2: second predetermined period, TA: predetermined temperature, Toil: oil temperature, ΔNwf: front wheel differential rotation speed (difference in rotation speed between left and right drive wheels)

Claims

[Claim 1] A protection and control device for a differential gear device that absorbs a rotational speed difference between left and right drive wheels of a vehicle, a stuck determination unit that determines whether the vehicle is in a stuck state in which driving force has been lost; a differential continuation determination unit that, when the stuck determination unit determines that the vehicle is in a stuck state, determines whether or not the vehicle is in a differential continuation state in which the oil temperature in the differential gear device is equal to or lower than a predetermined temperature, the accumulated heat generation amount of the differential gear device over a first predetermined period is equal to or greater than a predetermined heat generation amount, and the rotational speed difference between the left and right drive wheels is equal to or greater than a predetermined threshold value and has continued for equal to or greater than a second predetermined period; an output suppression control unit that suppresses a drive output of the vehicle when the differential continuation determination unit determines that the differential continuation state is present. A protection and control device for a differential gear device.

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